Solution:1

Maybe you want to give a chance to Yakuake (KDE based, running natively on Gnome), which embeds a drop down terminal emulator at the very top of your screen, and this can be invoked by pressing a custom key (ussually F12).

Yakuake, similar to Guake, runs in the background and it's available and ready when you need it in a key press. You can configure if you wish it in the foreground or it can lose focus as a common window.

I personally prefer the usage of Yakuake instead of Guake as I find it fully configurable and easy to set my preferences. It also features "terminal-splitting" on which you can create your custom layout for several terminals running different processes at once, like these shown in this screenshot:

Additionally, you can have an unlimited number of terminal sessions running at once, each one with its own custom layout.

Good luck!

Solution:2

I like tilda a lot. It's a drop-down terminal toggled with a single key shortcut. It is highly customizable, but what I like most about it is that it perfectly blends visually into Ubuntu Desktop.